Wireless power receiver coil for implantable neuromodulation device

ABSTRACT

The present disclosure relates to implantable neuromodulation devices, and in particular to a wireless power coil for a neuromodulation device that is to be implanted in a minimally invasive manner, for example, through a trocar or cannula. Particularly, aspects of the present disclosure are directed to a medical device that includes a lossy housing surrounding a power supply, and a receiving coil configured to exchange power wirelessly via a wireless power transfer signal and deliver the power to the power supply. The receiving coil is spaced a predetermined distance from the lossy housing. The medical device further includes a gap provided between the lossy housing and the receiving coil on a vertical plane, and a spacer that fills in at least a portion of the gap to maintain the lossy housing a predetermined distance from the receiving coil.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority and benefit from U.S.Provisional Application No. 62/730,106, filed Sep. 12, 2018, entitled“WIRELESS POWER RECEIVER COIL FOR IMPLANTABLE NEUROMODULATION DEVICE”,the entire contents of which are incorporated herein by reference forall purposes.

FIELD OF THE INVENTION

The present disclosure relates to implantable neuromodulation devices,and in particular to a wireless power coil for a neuromodulation devicethat is to be implanted in a minimally invasive manner, for example,through a trocar or cannula.

BACKGROUND

Normal neural activity is an intricate balance of electrical andchemical signals, which can be disrupted by a variety of insults(genetic, chemical or physical trauma) to the nervous system, causingcognitive, motor and sensory impairments. Similar to the way a cardiacpacemaker or defibrillator corrects heartbeat abnormalities,neuromodulation therapies help to reestablish normal neural balance. Inparticular instances, neuromodulation therapies utilize medical devicetechnologies to enhance or suppress activity of the nervous system forthe treatment of disease. These technologies include implantable as wellas non-implantable neuromodulation devices and systems that deliverelectrical, chemical or other agents to reversibly modify brain andnerve cell activity. The most common neuromodulation therapy is spinalcord stimulation to treat chronic neuropathic pain. In addition tochronic pain relief, some examples of neuromodulation therapies includedeep brain stimulation for essential tremor, Parkinson's disease,dystonia, epilepsy and psychiatric disorders such as depression,obsessive compulsive disorder and Tourette syndrome; sacral nervestimulation for pelvic disorders and incontinence; vagus nervestimulation for rheumatoid arthritis; gastric and colonic stimulationfor gastrointestinal disorders such as dysmotility or obesity; vagusnerve stimulation for epilepsy, obesity or depression; carotid arterystimulation for hypertension, and spinal cord stimulation for ischemicdisorders such as angina and peripheral vascular disease.

Neuromodulation devices and systems tend to have a similar form factor,derived from their predecessors, e.g. the pacemaker or defibrillator.Such neuromodulation devices and systems typically comprise an implantdevice including a neurostimulator having electronics connected to alead assembly that delivers electrical pulses to electrodes interfacedwith nerves or nerve bundles via an electrode assembly. In order tosupply energy to the neurostimulator an energy source such as anelectrochemical cell or a battery is typically arranged in theneurostimulator (e.g., within the housing of the neurostimulator).However, electrochemical cells and batteries have a limited life time.After the electrochemical cell or battery has been emptied ordischarged, it has to be re-charged or replaced when the energy storedis not sufficient for the physiological treatment. In the case of animplanted device such as a neurostimulator it is for several reasonspreferred to recharge an electrochemical cell or battery rather thanreplacing the cell or battery. One reason is the invasive natureassociated with removal and replacement of the energy source and therisk to the patient. Other reasons include that some implanted devicesconsume a relatively large amount of energy and would then have to havetheir energy sources replaced relatively often, which can beinconvenient and costly for the patient.

One of the non-invasive methods to recharge the electrochemical cell orbattery is through wireless power transfer. This method comprises anexternal power charger and a power receiver embedded into the implantdevice. The power receiver is typically made by a coil of wire connectedto power management circuitry. However, in the case of implant devicesmeant for both subcutaneous and deeper point applications, the implantdevices are typically characterized by a very low thickness profile andimplanted via a minimally invasive manner, for example, through a trocaror cannula. Given the very low thickness profile of the implant devicesand the small diameter of the trocar or cannula, the coil is oftenplaced next to other components such as metal enclosures for electroniccircuitry, which reduces the wireless power transfer efficiency. Thus,wasting energy, requiring longer charge times and/or more frequentcharging sessions. In view of these inefficiencies, it is desirable todevelop neuromodulation devices and systems that are capable of havingdesign flexibility, and desirable mechanical properties to increase thewireless power transfer efficiency.

BRIEF SUMMARY

In various embodiments, a medical device is provided that includes: alossy housing surrounding a power supply; and a receiving coilconfigured to exchange power wirelessly via a wireless power transfersignal and deliver the power to the power supply. The receiving coil isspaced a predetermined distance from the lossy housing; and thepredetermined distance is determined based on: (i) a size constraint ofa delivery mechanism for the medical device, (ii) a size of the lossyhousing, (iii) an area of the receiving coil, and (iv) a coupling factorbetween the receiving coil and a transmitting coil of greater than 0.5.

In some embodiments, the delivery mechanism is another medical devicecomprising a lumen defined by the size constraint, and wherein themedical device has a size configured to fit within the size constraintof the lumen such that the medical device can be implanted in a patientthrough the delivery mechanism. Optionally, the delivery mechanism is alaparoscopic port.

In some embodiments, the size of the medical device includes a width ofless than 24 mm, a height of less than 15 mm, and a length of less than80 mm. In some embodiments, the size of the lossy housing includes awidth of less than 24 mm, a height of less than 10 mm, and a length ofless than 80 mm. In some embodiments, the receiving coil has a qualityfactor of greater than 50. In some embodiments, the receiving coil has aquality factor of greater than 100.

In some embodiments, the receiving coil is comprised gold (Au),gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium(Ti), gold/titanium (Au/Ti), or any alloy thereof. In some embodiments,the housing is comprised of metal. Optionally, the metal is titanium oran alloy thereof.

In some embodiments, the predetermined distance is from 250 μm to 20 mm.In some embodiments, the size constraint of the delivery mechanismincludes a diameter of less than 30 mm. In some embodiments, the sizeconstraint of the delivery mechanism includes a width of less than 30mm, a height of less than 30 mm, and a length of less than 250 mm. Insome embodiments, the area of the receiving coil is determined based on:(i) the size constraint of the delivery mechanism, (ii) the size of thelossy housing, and (iii) the coupling factor between the receivingconductor structure and the transmitting conductor structure of greaterthan 0.5.

In some embodiments, the receiving coil has a height that is determinedbased on: (i) a height or diameter of the size constraint, (ii) a heightof the lossy housing, and (iii) the predetermined distance. In someembodiments, the receiving coil has a width that is determined based on:(i) a width or diameter of the size constraint. In some embodiments, thereceiving coil has a length that is determined based on: (i) a length ofthe size constraint. In some embodiments, the area of the receiving coilis determined based on: (i) the height of the receiving coil, (ii) thewidth of the receiving coil, (iii) the length of the receiving coil, and(iv) the coupling factor between the receiving coil and the transmittingcoil of greater than 0.5.

In various embodiments, a medical device is provided that includes ahousing; a power supply within the housing and connected to anelectronics module; and a receiving coil configured to exchange powerwirelessly via a wireless power transfer signal and deliver the power tothe power supply. The receiving coil is a helical structure comprising afirst turn, a last turn, and one or more turns disposed between thefirst turn and the last turn; and a width of the first turn is less thana width of the last turn.

In some embodiments, the one or more turns have a sequential increase inwidth from the first turn to the last turn such that a shape of thereceiving coil is a pyramid. In some embodiments, the receiving coil isspaced a predetermined distance from the housing, and wherein thepredetermined distance is determined based on: (i) a size constraint ofa delivery mechanism for the medical device, (ii) a size of the housing,(iii) an area of the receiving coil, and (iv) a coupling factor betweenthe receiving coil and a transmitting coil of greater than 0.5.Optionally, the delivery mechanism is another medical device comprisinga lumen defined by the size constraint, and wherein the medical devicehas a size configured to fit within the size constraint of the lumensuch that the medical device can be implanted in a patient through thedelivery mechanism. Optionally, the delivery mechanism is a laparoscopicport.

In some embodiments, the receiving coil has a height that is determinedbased on: (i) a pitch between each turn of the receiving coil, (ii) aheight or diameter of the size constraint, (iii) a height of thehousing, and (iv) the predetermined distance. In some embodiments, thereceiving coil has a width that is determined based on: (i) a width ordiameter of the size constraint. In some embodiments, the receiving coilhas a length that is determined based on: (i) a length of the sizeconstraint. In some embodiments, the area of the receiving coil isdetermined based on: (i) the height of the receiving coil, (ii) thewidth of the receiving coil, (iii) the length of the receiving coil, and(iv) the coupling factor between the receiving coil and the transmittingcoil of greater than 0.5.

In various embodiments, a wireless power transfer system is providedcomprising: a transmitting conductive structure configured to exchangepower wirelessly via a wireless power transfer signal; and a receivingconductive structure integrated into a lossy environment comprising alossy component, wherein the receiving conductive structure isconfigured to exchange power wirelessly with the transmitting conductivestructure via the wireless power transfer signal. The receivingconductive structure is spaced a predetermined distance from the lossycomponent; and the predetermined distance is determined based on: (i) asize constraint of a delivery mechanism for the lossy environment, (ii)a size of the lossy component, (iii) an area of the receiving conductivestructure, and (iv) a coupling factor between the receiving conductivestructure and a transmitting conductive structure of greater than 0.5.

In some embodiments, the transmitting conductive structure and thereceiving conductive structure have a quality factor of greater than 50.In some embodiments, the transmitting conductive structure and thereceiving conductive structure have a quality factor of greater than100.

In some embodiments, the transmitting conductive structure and thereceiving conductive structure are comprised of gold (Au), gold/chromium(Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti),gold/titanium (Au/Ti), or any alloy thereof. In some embodiments, thelossy component is comprised of metal. Optionally, the metal is titaniumor an alloy thereof.

In some embodiments, the predetermined distance is from 250 μm to 20 mm.In some embodiments, the receiving conductive structure is a helicalstructure comprising a first turn, a last turn, and one or more turnsdisposed between the first turn and the last turn; and wherein a widthof the first turn is less than a width of the last turn. In someembodiments, the area of the receiving conductive structure isdetermined based on: (i) the size constraint of the delivery mechanism,(ii) the size of the lossy component, and (iii) the coupling factorbetween the receiving conductor structure and the transmitting conductorstructure of greater than 0.5.

In various embodiments, a medical device is provided comprising: ahousing; a power supply within the housing and connected to anelectronics module; and a receiving coil configured to exchange powerwirelessly via a wireless power transfer signal and deliver the power tothe power supply. The receiving coil is a two-dimensional or planarstructure comprising a one or more conductive traces formed on asubstrate; and the two-dimensional or planar structure is rolled up intoa three-dimensional structure.

In some embodiments, a size of the three-dimensional structure isdetermined based on: (i) a size constraint of a delivery mechanism forthe medical device, (ii) a size of the housing, (iii) an area of thereceiving coil, and (iv) a coupling factor between the receiving coiland a transmitting coil of greater than 0.5. In some embodiments, theone or more conductive traces are formed with a predetermined shape onthe substrate. Optionally, the predetermined shape is a spiral.

In some embodiments, the delivery mechanism is another medical devicecomprising a lumen defined by the size constraint, and wherein themedical device has a size configured to fit within the size constraintof the lumen such that the medical device can be implanted in a patientthrough the delivery mechanism. Optionally, the delivery mechanism is alaparoscopic port.

In various embodiments, a neuromodulation system is provided including:a transmitting conductive structure configured to exchange powerwirelessly via a wireless power transfer signal; and an implantableneurostimulator including: a lossy housing; a connector attached to ahole in the lossy housing; one or more feedthroughs that pass throughthe connector; an electronics module within the lossy housing andconnected to the one or more feedthroughs; a power supply within thelossy housing and connected to the electronics module; and a receivingconductive structure disposed outside of the housing and connected tothe power supply. The receiving conductive structure is configured toexchange power wirelessly with the transmitting conductive structure viathe wireless power transfer signal and deliver the power to the powersupply; the receiving conductive structure is spaced a predetermineddistance from the lossy housing; and the predetermined distance isdetermined based on: (i) a size constraint of a delivery mechanism forthe neuromodulation system, (ii) a size of the lossy housing, (iii) anarea of the receiving conductive structure, and (iv) a coupling factorbetween the receiving conductive structure and a transmitting conductivestructure of greater than 0.5. The neuromodulation system may furtherinclude a lead assembly including: a lead body including a conductormaterial; a lead connector that connects the conductor material to theone or more feedthroughs; and one or more electrodes connected to theconductor material.

In some embodiments, the size constraint of the implantableneurostimulator includes a width of less than 24 mm, a height of lessthan 15 mm, and a length of less than 80 mm. In some embodiments, thearea of the receiving conductive structure is determined based on: (i)the size constraint of the delivery mechanism, (ii) the size of thelossy component, and (iii) the coupling factor between the receivingconductor structure and the transmitting conductor structure of greaterthan 0.5.

In some embodiments, the transmitting conductive structure and thereceiving conductive structure have a quality factor of greater than 50.In some embodiments, the transmitting conductive structure and thereceiving conductive structure have a quality factor of greater than100.

In some embodiments, the transmitting conductive structure and thereceiving conductive structure are comprised of gold (Au), gold/chromium(Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti),gold/titanium (Au/Ti), or any alloy thereof. In some embodiments, thelossy housing is comprised of metal. Optionally, the metal is titaniumor an alloy thereof. In some embodiments, the predetermined distance isfrom 250 μm to 20 mm. In some embodiments, the receiving conductivestructure is a helical structure comprising a first turn, a last turn,and one or more turns disposed between the first turn and the last turn;and wherein a width of the first turn is less than a width of the lastturn.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood in view of the followingnon-limiting figures, in which:

FIG. 1 shows an shows a neuromodulation system in accordance withvarious embodiments;

FIG. 2 shows a wireless power transfer system in accordance with variousembodiments;

FIGS. 3A-3F show a neurostimulator with a wireless power receiver coilin accordance with various embodiments;

FIGS. 4A-4F show a wireless power receiver coil with a three-dimensionalstructure in accordance with various embodiments; and

FIGS. 5A-4E show a wireless power receiver coil with a two-dimensionalstructure that can be rolled into a three-dimensional structure inaccordance with various embodiments.

DETAILED DESCRIPTION I. Introduction

The following disclosure describes a wireless power coil for aneuromodulation device that is to be implanted in a minimally invasivemanner, for example, through a trocar or cannula. The basic principle ofan inductively coupled power transfer system includes a transmitter coiland a receiver coil. Both coils form a system of magnetically coupledinductors. An alternating current in the transmitter coil generates amagnetic field which induces a voltage in the receiver coil. Byattaching a load to the receiver coil the voltage can be used to poweran electronic device or charge a battery. The magnetic field generatedby the transmitter coil radiates (approximately equally) in alldirections, hence the flux drops rapidly with distance (obeying aninverse square law). Consequently, the receiver coil must be placed asclose as possible to the transmitter coil (less than 10 mm) to interceptthe most flux. This requirement of a close proximity between thetransmitter coil and the receiver coils is not always practical forneuromodulation therapy, especially instances in which theneurostimulator is implanted deeper than the subcutaneous layer (e.g.,within the brain or thoracic cavity).

Alternative, wireless charging systems have been developed that transferpower between a transmitter coil and a receiver coil that are operatingat identical resonant frequencies (determined by the coils' distributedcapacitance, resistance and inductance). The basic premise is that theenergy “tunnels” from one coil to the other instead of radiating in alldirections from the primary coil; and thus resonant wireless charging isnot governed by the inverse square law. This technique is still“inductive” in that the oscillating magnetic field generated by thetransmitter coil induces a current in the receiver coil and takesadvantage of the strong coupling that occurs between resonant coils evenwhen separated by tens of centimeters. Resonant wireless chargingaddresses the main drawbacks of inductive wireless charging, which isthe requirement to closely couple the coils and the demand for precisealignment from the user. However, resonant wireless charging is notwithout its own drawbacks. A primary drawback is a relatively lowefficiency due to flux leakage (even at close range a well-designedsystem might demonstrate an efficiency of 30% at 2 cm, dropping to 15%at 75 cm coil separation, greater circuit complexity and, because of the(typically) high operating frequencies, potential electromagneticinterference (EMI) challenges.

The efficiency of the power transfer in resonant wireless chargingdepends on the energy coupling rate between the coils and thecharacteristic parameters for each coil (i.e., inductor). The amount ofinductive coupling between coils is measured by their mutual inductance.The strength of the coupling may be expressed as a coupling factor,which is determined by the area of the coils including the distancebetween the coils, the ratio of width of the receiver coil/width of thetransmitter coil, the shape of the coils and the angle between thecoils. The characteristic parameters for each coil includes theresonance frequency and the intrinsic loss rate of the coils. A qualityfactor measures how well the system stores energy and is expressed asthe ratio of the resonance frequency matching between the coils and theintrinsic loss rate of the coils. A higher quality factor indicates alower rate of energy loss relative to the stored energy of the coils;the oscillations die out more slowly. Resonance allows the wirelesspower transfer system to operate at greater distances compared to anon-resonant one. However, frequency mismatch may be observed, which hasthe effect of limiting the maximum power stored and thus transferred.One factor that may influence the coupling factor and the quality factorof the coils is the external environment near the coils. In particular,the close proximity of an environmental factor such as metal or tissuehas been found to greatly influence the efficiency of the wireless powertransfer system.

Most conventional wireless power transfer systems involve transferringpower between a transmitting coil and a receiving coil in free spacewithout nearby environmental factors. Consequently, the best possibleefficiency of most conventional wireless power transmission systemsdepends on the coupling factor between the coils and the qualityfactors. However, for a low profile implanted device meant forsubcutaneous and deeper applications and implanted via a minimallyinvasive manner, for example, through a trocar or cannula, the variouscomponents of the neurostimulator are packed into a tight volume ofspace. In a low profile implanted device, this means that the receivingcoil will likely be placed next to a number of environmental factorsincluding the metal enclosure, which has been found to influence thecoupling (e.g., reduce the energy available to the receiving coil due toenergy absorption and change of field shape) and the quality factor ofthe coils (e.g., create a frequency mismatch).

To address these limitations and problems, it has been discovered thatto improve efficiency of the wireless power transfer in a system withenvironmental factors it is important to maintain sufficient spacingbetween the coils and the environmental factors. Given a fixed area orvolume for the delivery mechanism (e.g., trocar or cannula) of theimplantable device and wireless power transfer coil, maximizing the coilarea to maintain sufficient coupling and keeping enough spacing to avoidthe influence from the environmental factors means that it is importantto find a tradeoff between these requirements. One illustrativeembodiment of the present disclosure is directed to a medical devicethat comprises a lossy housing surrounding a power supply; and areceiving coil configured to exchange power wirelessly via a wirelesspower transfer signal and deliver the power to the power supply. Thereceiving coil is spaced a predetermined distance from the lossyhousing. The predetermined distance is determined based on: (i) a sizeconstraint of a delivery mechanism for the medical device, (ii) a sizeof the lossy housing, (iii) an area of the receiving coil, and (iv) acoupling factor between the receiving coil and a transmitting coil ofgreater than 0.5.

In other embodiments, a medical device is provided comprising: ahousing; power supply within the housing and connected to an electronicsmodule; and a receiving coil configured to exchange power wirelessly viaa wireless power transfer signal and deliver the power to the powersupply. The receiving coil is a helical structure comprising a firstturn, a last turn, and one or more turns disposed between the first turnand the last turn. A width of the first turn is less than a width of thelast turn. The one or more turns may have a sequential increase in widthfrom the first turn to the last turn such that a shape of the receivingcoil is a pyramid.

In other embodiments, a wireless power transfer system is providedcomprising a transmitting conductive structure configured to exchangepower wirelessly via a wireless power transfer signal; and a receivingconductive structure integrated into a lossy environment comprising alossy component. The receiving conductive structure is configured toexchange power wirelessly with the transmitting conductive structure viathe wireless power transfer signal. The receiving conductive structureis spaced a predetermined distance from the lossy component. Thepredetermined distance is determined based on: (i) a size constraint ofa delivery mechanism for the lossy environment, (ii) a size of the lossycomponent, (iii) an area of the receiving conductive structure, and (iv)a coupling factor between the receiving conductive structure and atransmitting conductive structure of greater than 0.5.

In other embodiments, a medical device is provided comprising: ahousing; power supply within the housing and connected to an electronicsmodule; and a receiving coil configured to exchange power wirelessly viaa wireless power transfer signal and deliver the power to the powersupply. The receiving coil is a two-dimensional or planar structurecomprising a one or more conductive traces formed on a substrate. Thetwo-dimensional or planar structure is rolled up into athree-dimensional structure.

In other embodiments, a neuromodulation system is provided comprising atransmitting conductive structure configured to exchange powerwirelessly via a wireless power transfer signal; an implantableneurostimulator including: a lossy housing; a connector attached to ahole in the lossy housing; one or more feedthroughs that pass throughthe connector; an electronics module within the lossy housing andconnected to the one or more feedthroughs; a power supply within thelossy housing and connected to the electronics module; and a receivingconductive structure disposed outside of the housing and connected tothe power supply. The receiving conductive structure is configured toexchange power wirelessly with the transmitting conductive structure viathe wireless power transfer signal and deliver the power to the powersupply. The receiving conductive structure is spaced a predetermineddistance from the lossy housing, and the predetermined distance isdetermined based on: (i) a size constraint of a delivery mechanism forthe neuromodulation system, (ii) a size of the lossy housing, (iii) anarea of the receiving conductive structure, and (iv) a coupling factorbetween the receiving conductive structure and a transmitting conductivestructure of greater than 0.5. The neuromodulation system furthercomprises a lead assembly including: a lead body including a conductormaterial; a lead connector that connects the conductor material to theone or more feedthroughs; and one or more electrodes connected to theconductor material.

Advantageously, these approaches provide a neuromodulation system, whichhas a very low thickness profile that is capable of being implanted in aminimally invasive manor, an efficient wireless power transfer, andgreater design flexibility. More specifically, these approaches enablefor spacing between the wireless power receiving coil and environmentalfactors presented by the neuromodulation system while also maximizingthe area of the wireless power receiving coil in order to maximize thewireless power transfer into the implanted neurostimulator.

II. Neuromodulation Devices and Systems with Wireless Power Transfer

FIG. 1 shows a neuromodulation system 100 in accordance with someaspects of the present invention. In various embodiments, theneuromodulation system 100 includes an implantable neurostimulator 105,a lead assembly 110, and a transmitting conductive structure 112 (e.g.,a transmitting coil). The implantable neurostimulator 105 may include ahousing 115, a connector 120, a power source 125, a receiving conductivestructure 130 (e.g., a wireless power coil or a receiving coil), anantenna 135, and an electronics module 140 (e.g., a computing system).The housing 115 may be comprised of materials that are biocompatiblesuch as bioceramics or bioglasses for radio frequency transparency, ormetals such as titanium or alloys thereof. In accordance with variousaspects, the size and shape of the housing 115 is selected such that theneurostimulator 105 can be implanted within a patient. In the exampleshown in FIG. 1, the connector 120 is attached to a hole in a surface ofthe housing 115 such that the housing 115 is hermetically sealed. Theconnector 120 may include one or more feedthroughs (i.e., electricallyconductive elements, pins, wires, tabs, pads, etc.) mounted within aheader and extending through the surface of the header from an interiorto an exterior of the header. The power source 125 (e.g., a battery) maybe within the housing 115 and connected (e.g., electrically connected)to the electronics module 140 to power and operate the components of theelectronics module 140. In some embodiments, the power source 125 andthe electronics module 140 are surrounded by the housing 115. Thewireless power coil 130 may be outside the housing 115 and configured toreceive electrical energy from the charging device 112. In someembodiments, the wireless power coil 130 is attached to an outsidesurface of the housing 115 by a spacer 142. The wireless power coil 130is connected (e.g., electrically connected) to the power source 125 toprovide the electrical energy to recharge or supply power to the powersource 125. The antenna 135 may be outside the housing 115 and connected(e.g., electrically connected) to the electronics module 140 forwireless communication with external devices via, for example,radiofrequency (RF) telemetry.

In some embodiments, the electronics module 140 may be connected (e.g.,electrically connected) to interior ends of the connector 120 such thatthe electronics module 140 is able to apply a signal or electricalcurrent to conductive traces of the lead assembly 110 connected toexterior ends of the connector 120. The electronics module 140 mayinclude discrete and/or integrated electronic circuit components thatimplement analog and/or digital circuits capable of producing thefunctions attributed to the neuromodulation devices or systems such asapplying or delivering neural stimulation to a patient. In variousembodiments, the electronics module 140 may include software and/orelectronic circuit components such as a pulse generator 145 thatgenerates a signal to deliver a voltage, current, optical, or ultrasonicstimulation to a nerve or artery/nerve plexus via electrodes, acontroller 150 that determines or senses electrical activity andphysiological responses via the electrodes and sensors, controlsstimulation parameters of the pulse generator 145 (e.g., controlstimulation parameters based on feedback from the physiologicalresponses), and/or causes delivery of the stimulation via the pulsegenerator 145 and electrodes, and a memory 155 with program instructionsoperable on by the pulse generator 145 and the controller 150 to performone or more processes for applying or delivering neural stimulation.

In various embodiments, the lead assembly 110 is a monolithic structurethat includes a cable or lead body 160. In some embodiments, the leadassembly 110 further includes one or more electrode assemblies 165having one or more electrodes 170, and optionally one or more sensors.In some embodiments, the lead assembly 110 further includes a leadconnector 175. In certain embodiments, the lead connector 175 is bondingmaterial that bonds conductor material of the lead body 160 to theelectronics module 140 of the implantable neurostimulator 105 via theconnector 120. The bonding material may be a conductive epoxy or ametallic solder or weld such as platinum. In other embodiments, the leadconnector 175 is conductive wire, conductive traces, or bond pads (e.g.,a wire, trace, or bond pads formed of a conductive material such ascopper, silver, or gold) formed on a substrate and bonds a conductor ofthe lead body 160 to the electronics module 140 of the implantableneurostimulator 105. In alternative embodiments, the implantableneurostimulator 105 and the lead body 160 are designed to connect withone another via a mechanical connector 175 such as a pin and sleeveconnector, snap and lock connector, flexible printed circuit connectors,or other means known to those of ordinary skill in the art.

The conductor material of the lead body 160 may be one or moreconductive traces 180 formed on a supporting structure 185. The one ormore conductive traces 180 allow for electrical coupling of theelectronics module 140 to the electrodes 170 and/or sensors of theelectrode assemblies 165. The supporting structure 185 may be formedwith a dielectric material such as a polymer having suitable dielectric,flexibility and biocompatibility characteristics. Polyurethane,polycarbonate, silicone, polyethylene, fluoropolymer and/or othermedical polymers, copolymers and combinations or blends may be used. Theconductive material for the traces 180 may be any suitable conductorsuch as stainless steel, silver, copper or other conductive materials,which may have separate coatings or sheathing for anticorrosive,insulative and/or protective reasons.

The electrode assemblies 165 may include the electrodes 170 and/orsensors fabricated using various shapes and patterns to create certaintypes of electrode assemblies (e.g., book electrodes, split cuffelectrodes, spiral cuff electrodes, epidural electrodes, helicalelectrodes, probe electrodes, linear electrodes, neural probe, paddleelectrodes, intraneural electrodes, etc.). In various embodiments, theelectrode assemblies 165 include a base material that provides supportfor microelectronic structures including the electrodes 170, a wiringlayer, optional contacts, etc. In some embodiments, the base material isthe supporting structure 185. The wiring layer may be embedded within orlocated on a surface of the supporting structure 185. The wiring layermay be used to electrically connect the electrodes 170 with the one ormore conductive traces 180 directly or indirectly via a lead conductor.The term “directly”, as used herein, may be defined as being withoutsomething in between. The term “indirectly”, as used herein, may bedefined as having something in between. In some embodiments, theelectrodes 170 may make electrical contact with the wiring layer byusing the contacts.

III. Wireless Power Transfer System

FIG. 2 shows a wireless power transfer system 200 comprising atransmitting device 205 and a receiving device 210 spaced apart from oneanother by a distance (D). In some embodiments, the transmitting device205 is connected to a power supply 215 such a main power line. Thetransmitting device 205 is configured to convert input power (DC or ACelectric current) from the power supply 215 into a wireless powertransfer signal 220. For example, the input power is converted into thewireless power transfer signal 220 by a first coupling device 225. Insome embodiments, the wireless power transfer signal 220 is a timevarying electromagnetic field. The receiving device 210 is configured toreceive the wireless power transfer signal 220, convert the wirelesspower transfer signal 220 into an output power (AC or DC electriccurrent), and deliver the output power to a load 230 (e.g., the powersource 125 described with respect to FIG. 1). For example, the wirelesspower transfer signal 220 is converted into the output power by a secondcoupling device 235. Accordingly, the second coupling device 235 isconfigured to exchange power wirelessly with the first coupling device225 via the wireless power transfer signal 220.

In some embodiments, the first coupling device 225 includes an optionaloscillator 240 and a transmitting conductive structure 245 (e.g., atransmitting conductive structure 112 described with respect to FIG. 1).In some embodiments, the transmitting conductive structure 245 is atransfer coil of wire configured to exchange power wirelessly via thewireless power transfer signal 220. The oscillator 240 may be used togenerate a high frequency AC current, which drives the transmittingconductive structure 245 to generate the wireless power transfer signal220 such as the time varying or oscillating electromagnetic field. Insome embodiments, the second coupling device 235 includes an optionalrectifier 250 and a receiving conductive structure 255 (e.g., areceiving conductive structure 130 described with respect to FIG. 1). Insome embodiments, the receiving conductive structure 255 is a receivingcoil of wire configured to exchange power wirelessly with thetransmitting conductive structure 245 via the wireless power transfersignal 220. The rectifier 250 may be used to convert the AC currentinduced at the receiving conductive structure 255 into DC current, whichis delivered to the load 235. In some embodiments, the transmittingconductive structure 245 and the receiving conductive structure 255 havea quality factor of greater than 50. In other embodiments, thetransmitting conductive structure 245 and the receiving conductivestructure 255 have a quality factor of greater than 100.

In some embodiments, the first coupling device 225 further includes aresonant circuit 260 which includes: (i) the transmitting conductivestructure 245 connected to a capacitor 265, (ii) the transmittingconductive structure 245 being a self-resonant coil; or (iii) anotherresonator (not shown) with internal capacitance. In some embodiments,the second coupling device 235 further includes a resonant circuit 270which includes: (i) the receiving conductive structure 255 connected toa capacitor 275, (ii) the receiving conductive structure 255 being aself-resonant coil; or (iii) another resonator (not shown) with internalcapacitance. The first coupling device 225 and the second couplingdevice 235 are tuned to resonate at a same resonant frequency. Theresonance between the transmitting conductive structure 245 and thereceiving conductive structure 255 may increase coupling and moreefficient power transfer.

In various embodiments, the receiving conductive structure 255 is in alossy environment 280. As used herein “lossy” means having or involvingthe dissipation of electrical or electromagnetic energy. In someembodiments, the lossy environment 280 includes one or more lossyenvironmental factors or components 285, which result in current lossduring the wireless power transfer between the transmitting conductivestructure 245 and the receiving conductive structure 255. In someembodiments, the lossy environment 280 is an implantable medical devicesuch as a neurostimulator as described with respect to FIG. 1. In someembodiments, the one or more lossy environmental factors or components285 include body fluid, body tissue, a lossy component of theimplantable medical device, or a combination thereof. In certainembodiments, the lossy component of the medical device is a housingcomprised of metal. In some embodiments, the metal is titanium or analloy thereof.

IV. Wireless Power Coil

FIGS. 3A, 3B, and 3C show an implantable device 300 (e.g., theimplantable neurostimulator 105 described with respect to FIG. 1)comprising a receiving conductive structure 305 (e.g., the receivingconductive structure 255 described with respect to FIG. 2) in accordancewith aspects of the present disclosure. In various embodiments, a sizeof the implantable device 300 is constrained small enough such that thedevice can be implanted in a less complex and minimally invasive manner,for example, through a delivery mechanism 310. In some embodiments, thedelivery mechanism 310 is another medical device (a medical devicedifferent from the implantable device 300) comprising a lumen defined bya size constraint 315. The implantable device 300 may be implanted in apatient through the lumen of the delivery mechanism 310. In someembodiments, the implantable device 300 has a size including: (i) awidth (w) of less than 24 mm, for example from 10 mm to 20 mm, (ii) aheight (h) of less than 15 mm, for example from 5 mm to 13 mm, and (iii)a length (l) of less than 80 mm, for example from 20 mm to 40 mm.

In various embodiments, the receiving conductive structure 305 isphysically configured to exchange power wirelessly via a wireless powertransfer signal and deliver the power to the power supply. Physicallyconfigured means the receiving conductive structure 305 includes: (i)inductance and power receiving capability to meet the needs of theimplantable device 300 including the ability to transfer power to thepower source with at least an 8% overall efficiency; (ii) the mechanicaldimensions (e.g., the height, width and length of the receivingconductive structure 305) fit to the size constraint 315 of the deliverymechanism 310 for the implantable device 300; (iii) the receivingconductive structure 305 is spaced apart from environmental factors tosufficiently avoid coupling of power to the environmental factors; and(iv) the receiving conductive structure 305 is biocompatible and adurable construction for the implanted environment.

In some embodiments, the receiving conductive structure 305 is areceiving coil comprising wound wire. In certain embodiments, the wireis formed from a conductive material. The conductive material may becomprised of various metals or alloys thereof, for example, gold (Au),gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium(Ti), gold/titanium (Au/Ti), or any alloy thereof. In some embodiments,the coil has an inductance ranging from 0.5 uH to 50 uH or from 1 uH to15 uH, for example about 1.2 uH. In some embodiments, the coil has aworking frequency ranging from 1 mHz to 100 mHz or from 3 mHz to 50 mHz,for example about 27.12 mHz (ISM Standard Frequency). In someembodiments, the coil has a working voltage ranging from 5 V to 50 V orfrom 10 V to 35 V, for example about 25 V. In some embodiments, the wireof the coil has an American Wire Gauge (AWG) ranging from 25 AWG to 40AWG or from 28 AWG to 37 AWG, for example 32 AWG. As used herein, theterms “substantially,” “approximately” and “about” are defined as beinglargely but not necessarily wholly what is specified (and include whollywhat is specified) as understood by one of ordinary skill in the art. Inany disclosed embodiment, the term “substantially,” “approximately,” or“about” may be substituted with “within [a percentage] of” what isspecified, where the percentage includes 0.1, 1, 5, and 10 percent.

FIGS. 3A, 3B, and 3C show the implantable device 300 may furthercomprise a lossy housing 320 and optionally a connector 325 attached toan electronics module through a hole 330 in the lossy housing 320 (e.g.,the housing 115 and connector 120 described with respect to FIG. 1). Invarious embodiments, an epoxy covers at least a portion of theimplantable device 300 in order to hold the components together andprotect the components from environmental factors such as biologicalfluid. The epoxy may be a resin comprising one or more low molecularweight pre-polymers, one or more higher molecular weight polymers, orcombinations thereof, which comprise at least two epoxide groups. Insome embodiments, the epoxy covers substantially, if not entirely, theentire device 300 (e.g., the receiving conductive structure 305, thelossy housing 320, the connector 325, and hole 330 are covered). Inother embodiments, the epoxy covers select components of the device 300but not all of the components (e.g., at least the receiving conductivestructure 305, the connector 325, and the hole 330 are covered while thelossy housing is exposed). In some embodiments, the lossy housing 320 iscomprised of materials that are biocompatible such as bioceramics orbioglasses for radio frequency transparency, or metals such as titaniumor an alloy thereof. In some embodiments, the lossy housing 320 has asize including: (i) a width (w′) of less than 24 mm, for example from 10mm to 20 mm, (ii) a height (h′) of less than 10 mm, for example from 5mm to 9 mm, and (iii) a length (l′) of less than 80 mm, for example from20 mm to 40 mm.

As described herein, the lossy housing 320 may be an environmentalfactor that may influence performance of the receiving conductivestructure 305 and thus the performance of the wireless power transfersystem. In order to minimize the influence of the lossy housing 320 onthe performance of the receiving conductive structure 305, the receivingconductive structure 305 is spaced a predetermined distance (s) from thelossy housing 320. However, the predetermined distance (s) is notboundless as in free space, and instead the predetermined distance (s)is bounded by one or more factors including the size of the implantabledevice 300, the size of the lossy housing 320, the size constraint 310of the delivery mechanism 315, an area 335 of the receiving conductivestructure 305, a requirement to minimize coupling of power from thereceiving conductive structure 305 to the lossy housing 320, and arequirement to limit a shift in the resonance frequency or decrease inthe quality factor of the receiving conductive structure 305.

In some embodiments, the predetermined distance (s) is determined basedon: (i) the size constraint 315 of the delivery mechanism 310 for theimplantable device 300, (ii) the size of the lossy housing 320, (iii)the area 335 of the receiving conductive structure 305, and (iv) acoupling factor between the receiving conductive structure 305 and thetransmitting conductive structure of greater than 0.5. In someembodiments, the predetermined distance (s) is less than or equal to 5mm, from 250 μm to 5 mm, from 250 μm to 20 mm, or from 500 μm to 15 mm,for example about 8 mm. As used herein, when an action or element is“triggered by” or “based on” something, this means the action or elementis triggered or based at least in part on at least a part of thesomething. In some embodiments, the predetermined distance (s) providesa gap between the lossy housing 320 and the receiving conductivestructure 305 on a vertical plane. In some embodiments, thepredetermined distance (s) or gap between the receiving conductivestructure 305 and the lossy housing 320 is maintained with a spacer orcovering 340 that is comprised of a medical grade polymer material. Incertain embodiments, the spacer or covering 340 fills in at least aportion of the gap to maintain the lossy housing 320 the predetermineddistance (s) from the receiving conductive structure 305. In someembodiments, the spacer or covering 340 surrounds the receivingconductive structure 305 and fills in at least a portion of the gapcreated by the predetermined distance (s) between the receivingconductive structure 305 and the lossy housing 320. In otherembodiments, the spacer or covering 340 is attached to one or moresurfaces of the receiving conductive structure 305 and fills in at leasta portion of the gap created by the predetermined distance (s) betweenthe receiving conductive structure 305 and the lossy housing 320. Themedical grade polymer may be thermosetting or thermoplastic. Forexample, the medical grade polymer may be a soft polymer such assilicone, a polymer dispersion such as latex, a chemical vapor depositedpoly(p-xylylene) polymer such as parylene, or a polyurethane such asBionate® Thermoplastic Polycarbonate-urethane (PCU) or CarboSil®Thermoplastic Silicone-Polycarbonate-urethane (TSPCU).

FIG. 3C shows that determining the predetermined distance (s) involves atradeoff between increasing the predetermined distance (s), whichminimizes coupling of power from the receiving conductive structure 305to the lossy housing 320, while maintaining a sufficient area 335 forthe receiving conductive structure 305 in the size constraint 310 of thedelivery mechanism 315 to ultimately achieve a coupling factor betweenthe receiving conductive structure 305 and the transmitting conductivestructure of greater than 0.5. The coupling factor is generallydetermined by the distance (D) between the receiving conductivestructure 305 and the transmitting conductive structure and the areaencompassed by the receiving conductive structure 305 and thetransmitting conductive structure. For example, the greater the amountof the wireless power transfer signal (e.g., the greater the amount offlux from the magnetic field) that reaches the receiving conductivestructure 305, the better the conductive structures are coupled and thehigher the coupling factor. The amount of the wireless power transfersignal that reaches the receiving conductor structure 305 may beincreased by increasing the area 335 of the receiving conductorstructure 305. However, the coupling factor may be decreased by thepresence of an environmental factor such as the housing 320, which maycouple with the receiving conductive structure 305 and leach power thatis being transferred to the receiving conductive structure 305.

As shown in FIG. 3C, the implantable device 300 has a size configured tofit within the size constraint 315 of the delivery mechanism 310. Insome embodiments, the size of the implantable device 300 includes: (i) awidth (w) of less than 24 mm, for example from 5 mm to 15 mm or about 6mm, (ii) a height (h) of less than 15 mm, for example from 5 mm to 13mm, and (iii) a length (l) of less than 80 mm, for example from 20 mm to40 mm or about 35 mm. In certain embodiments, the size of theimplantable device 300 includes a width (w) of less than 24 mm, a height(h) of less than 15 mm, and a length (l) of less than 80 mm. In someembodiments, the size of the lossy housing 320 includes: (i) a width(w′) of less than 24 mm, for example from 10 mm to 20 mm, (ii) a height(h′) of less than 10 mm, for example from 5 mm to 9 mm, and (iii) alength (l′) of less than 80 mm, for example from 20 mm to 40 mm. Incertain embodiments, the size of the lossy housing 320 includes a width(w′) of less than 24 mm, a height (h′) of less than 10 mm, and a length(l′) of less than 80 mm. In some embodiments, the size constraint 315 ofthe delivery mechanism 310 includes: (i) a width (w″) of less than 30mm, for example from 10 mm to 20 mm, (ii) a height (h″) of less than 30mm, for example from 10 mm to 20 mm, and (iii) a length (l″) of lessthan 250 mm, for example from 40 mm to 100 mm. In certain embodiments,the size constraint 310 includes a width of less than 30 mm, a height ofless than 30 mm, and a length of less than 250 mm.

In various embodiments, the delivery mechanism 320 is a laparoscopicport. A laparoscopic port for a minimally invasive procedure such asimplantation of the device 300 may be exemplified as a cannula device ora trocar. Trocars typically comprise an outer housing and seal assembly,a sleeve with a lumen that fits inside the housing and seal assembly anda piercing stylus (e.g., an obturator) which slots into the lumen suchthat the tip of the stylus protrudes from the lower end of the device.The stylus may be used to create an opening in the abdominal wallthrough which the sleeve is inserted and fixed into place, followingwhich the stylus is removed through an opening in the upper end of thedevice to allow insertion of a laparoscope or other surgical tools, orthe device 300 in accordance with various aspects disclosed herein,through the lumen. A wide range of laparoscopic cannula devices andtrocars exist having a variety of lengths and diameters. In someembodiments, the sleeve of the delivery mechanism 320 defines the sizeconstraint 315 (e.g., the area of the lumen) of the delivery mechanism320. In some embodiments, the size constraint 315 has a circularcross-section A-A, as shown in FIG. 3C. In certain embodiments, the sizeconstraint 315 comprises a diameter (d) (width (w″)=height (h″)) of lessthan 30 mm, for example from 10 mm to 20 mm.

While the circular cross-section of the size constraint 315 is describedherein in particular detail with respect to several describedembodiments, it should be understood that other shapes or cross-sectionsof the size constraint 315 have been contemplated without departing fromthe spirit and scope of the present invention. For example, the sizeconstraint 315 may have an oval, rounded rectangle, semi-rectangular,obround, or semi obround shape or cross-section. As used herein, theterm “semi-rectangular” or “semi-rectangular cross section” means arounded rectangular portion overlaid onto a larger central circularportion, as shown in FIG. 3D. As used herein, the term “roundedrectangle” or “rounded rectangular portion” means a shape obtained bytaking the convex surface of four equal circles of radius r and placingtheir centers at the four corners of a rectangle with side lengths a andb and creating a perimeterp around the surface of the four equal circlesand the rectangle, where the perimeterp of the shape is equal to2(a+b+πr), as shown in FIG. 3E. As used herein, the term “semi-obround”or “semi-obround cross section” means an obround portion overlaid onto alarger central circular portion, as shown in FIG. 3F.

As shown in FIG. 3C, the receiving conductor structure 305 has area 335defined by (ww)×(hh)×(ll). In some embodiments, the area 335 of thereceiving conductor structure 305 is determined based on: (i) the sizeconstraint 315 of the delivery mechanism 320, (ii) the size of the lossyhousing 325, and (iii) the coupling factor between the receivingconductor structure 305 and the transmitting conductor structure ofgreater than 0.5. In some embodiments, the width (ww) is determinedbased on: (i) the width (w″) or the diameter (d) of the size constraint315. In some embodiments, the length (ll) is determined based on: (i) alength (l″) of the size constraint 315. In some embodiments, the height(hh) is determined based on: (i) the height (h″) or the diameter (d) ofthe size constraint 315, (ii) the height (h″) of the lossy housing, and(iii) the predetermined distance (s). In order to increase the maximumpossible area 340 of the receiving conductor structure 305 to maintainthe coupling factor between the receiving conductor structure 305 andthe transmitting conductor structure of greater than 0.5 while alsoaccommodating for the predetermined distance (s), the height (hh) of thereceiving conductor structure 305 may be adjusted in a verticaldirection, the width (ww) of the receiving conductor structure 305 maybe adjusted in a horizontally direction, and the (ll) may also beadjusted in a horizontally direction.

As shown in FIG. 4A, in order to increase the maximum possible area ofthe receiving conductor structure 400 (e.g., the receiving conductorstructure 305 described with respect to FIGS. 3A, 3B, and 3C), thereceiving conductor structure 400 may be formed in a three-dimensionalmanner rather than the conventional two-dimensional or planar coil.Testing has revealed that a three-dimensional coil is capable ofmaintaining sufficient coupling (i.e., the coupling factor between thereceiving conductor structure 400 and the transmitting conductorstructure of greater than 0.5) and power transfer with the transmittingconductor structure in such an enlarged area. In some embodiments, thereceiving conductor structure 400 is a three-dimensional spiral orhelix. The helix includes characteristics designed to maximize the areaof the receiving conductor structure 400 in view of: (i) the sizeconstraint of the delivery mechanism, (ii) the size of the lossyhousing, and (iii) the coupling factor between the receiving conductorstructure 400 and the transmitting conductor structure of greater than0.5. In some embodiments, the characteristics of the helix include ashape 405, a number of turns 410, a pitch 415 (rise of the helix for oneturn), a helix angle 420, a helix length 425 (a length of the coil), atotal rise 430 of the helix (overall coil height (hh)), a width (ww), orcombinations thereof.

In some embodiments, the shape 405 of the coil is rounded rectangular.However, it should be understood that other shapes of the coil have beencontemplated without departing from the spirit and scope of the presentinvention. For example, the shape of the coil may be square,rectangular, circular, obround, etc. In some embodiments, the helix hasgreater than 2 turns or from 4 to 30 turns or from 4 to 15 turns, forexample 9 turns, and a pitch between each of the turns from 10 μm to 1cm or from 250 μm to 2 mm, for example about 500 μm. In someembodiments, the pitch between turns is the same or different. In someembodiments, the helix angle is from 5° to 85°, from 5° to 45°, or from7° to 25°, for example, about 20°. In some embodiments, the helix lengthis from 2 cm to 100 cm or 25 cm to 75 cm, e.g., about 50 cm, from afirst end 435 to a second end 440. In some embodiments, the total riseor overall coil height (hh) is less than 15 mm, for example from 5 mm to13 mm.

As shown in FIGS. 4B, 4C, 4D, and 4E, a width (ww) of each of the turns410 may be adjusted based on the position of the receiving conductorstructure 400 in the delivery mechanism 445 and the size constraint 450of the delivery mechanism 445. In various embodiments, a width (ww) ofeach of the turns 410 is less than or equal to a width of the lossyhousing (e.g., the width (w″) or the diameter (d) of the size constraint315). In some embodiments, a width (ww′) of the first turn 455 is lessthan a width (ww″) of the last turn 460 in order to accommodate thecurvature (i.e., the size constraint 450) of the delivery mechanism 445.In some embodiments, depending on the size constraint 450 of thedelivery mechanism 445 and the predetermined distance (s), the turns 465between the first turn 455 and the last turn 460 have a sequentialincrease in width (ww) from the first turn 455 such that a shape of thereceiving conductor structure 400 is a pyramid (see, e.g., FIGS. 4B and4C). In other embodiments, the width (ww′) of the first turn 455 is thesubstantially the same as the width (ww″) of the last turn 460 in orderto accommodate the curvature (i.e., the size constraint 450) of thedelivery mechanism 445. In some embodiments, depending on the sizeconstraint 450 of the delivery mechanism 445 and the predetermineddistance (s), the turns 465 between the first turn 455 and the last turn460 have a same, smaller, or larger width (ww) from that of the firstturn 455 or the last turn 460 such that a shape of the receivingconductor structure is configured to fit within the size constraint 450of the delivery mechanism 445 (see, e.g., FIGS. 4D and 4E).

In various embodiments, the number of turns 410 and the helix length 425are increased to maximize the area occupied by the receiving conductivestructure 400. In some embodiments, the number of turns 410 and thehelix length 425 are increased by adjusting the pitch 415, the helixangle 420, and the total rise 430. In some embodiments, as shown in FIG.4F, the receiving conductor structure 400 is a helical structure with atotal rise 430 or height that is determined based on: (i) a first pitch470 between a first turn 472 and a second turn 475 of the receivingconductor structure 400; (ii) a second pitch 480 between a last turn 482and a second to last turn 485 of the receiving conductor structure 400;and (iii) a third pitch 490 between remaining turns 495 between thesecond turn 475 and the second to last turn 485. The total rise 430 orheight may be determined further based on the size constraint 450 of thedelivery mechanism 445 and a size of the implantable device 497, inparticular, the height of the implantable device 497. For example, thetotal rise 430 or height of the receiving conductor structure 400 may bedetermined to be less than the difference of the diameter or height ofthe delivery mechanism 445 and the height of the implantable device 497.In some embodiments, the first pitch 470 and the second pitch 480 arefrom 10 μm to 3 mm or from 250 μm to 2 mm, for example about 500 μm; andthe third pitch 490 is from 500 μm to 1 cm or from 1 mm to 3 mm, forexample about 2 mm. In some embodiments, the first pitch 470 and thesecond pitch 480 are less than the third pitch 490. In some embodiments,the first pitch 470 is the same as the second pitch 480. In otherembodiments, the first pitch 470 is different from the second pitch 480.

Accordingly, by adjusting the width (ww) of each turn 410 and increasingthe total rise 430 or height of the receiving conductive structure 400it is possible to increase the number of turns 410 and the helix length425 to maximize the area occupied by the receiving conductive structure400. The area occupied by the receiving conductive structure 400 ismaximized while fitting the receiving conductive structure 400 withinthe sizing constraint 450 of the delivery mechanism 445 even with thepredetermined distance (s) between the lossy housing 498 and thereceiving conductive structure 400.

As shown in FIG. 5A, in order to increase the maximum possible area ofthe receiving conductor structure 500 (e.g., the receiving conductorstructure 305 described with respect to FIGS. 3A, 3B, and 3C), thereceiving conductor structure 500 may be formed as a two-dimensional orplanar coil 505. As shown in FIG. 5B, the two-dimensional or planar coil505 may be rolled up into a three-dimensional structure 510. In variousembodiments, the two-dimensional or planar coil 505 is rolled up into athree-dimensional structure 510 that is capable of fitting within thedelivery mechanism 515 in view of: (i) the size constraint 520 of thedelivery mechanism 515 and (ii) the size of the lossy housing 525 (see,e.g., FIGS. 5C and 5D). In some embodiments, a size of thethree-dimensional structure is determined based on: (i) a sizeconstraint of the delivery mechanism 515 for the implantable device,(ii) a size of the lossy housing 525, (iii) an area of the receivingconductor structure, and (iv) a coupling factor between the receivingconductor structure and a transmitting conductor structure of greaterthan 0.5. By rolling up the two-dimensional or planar coil 505 into thethree-dimensional structure 510 it is possible to deliver thetwo-dimensional or planar coil 505 via the delivery mechanism 515 to animplant site. As shown in FIG. 5E, once the implantable device 530 hasbeen delivered to the implant site via the delivery mechanism 515, thethree-dimensional structure 510 is capable of being unfurled back intothe two-dimensional or planar coil 505. Testing has revealed that oncethe two-dimensional or planar coil is unfurled it is capable ofmaintaining sufficient coupling (i.e., the coupling factor between thereceiving conductor structure 500 and the transmitting conductorstructure of greater than 0.5) and power transfer with the transmittingconductor structure in such an enlarged area.

In various embodiments, the receiving conductor structure 500 comprisesa substrate 535. In some embodiments, the substrate 535 is comprised ofone or more layers of dielectric material (i.e., an insulator). Thedielectric material may be selected from the group of electricallynonconductive materials consisting of organic or inorganic polymers,ceramics, glass, glass-ceramics, polyimide-epoxy, epoxy-fiberglass, andthe like. In certain embodiments, the dielectric material is a polymerof imide monomers (i.e., a polyimide), a liquid crystal polymer (LCP)such as Kevlar®, parylene, polyether ether ketone (PEEK), orcombinations thereof. In some embodiments, one or more conductive tracesor wirings 540 are formed on a portion of the substrate 535. As usedherein, the term “formed on” refers to a structure or feature that isformed on a surface of another structure or feature, a structure orfeature that is formed within another structure or feature, or astructure or feature that is formed both on and within another structureor feature.

In various embodiments, the one or more conductive traces 540 are aplurality of traces, for example, two or more conductive traces or fromtwo to twenty-four conductive traces. The plurality of conductive traces540 are comprised of one or more layers of conductive material. Theconductive material selected for the one or more conductive traces 550should have good electrical conductivity and may include pure metals,metal alloys, combinations of metals and dielectrics, and the like. Forexample, the conductive material may be gold (Au), gold/chromium(Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti),gold/titanium (Au/Ti), or any alloy thereof. The one or more conductivetraces 540 may be deposited onto a surface of the substrate 535 by usingthin film deposition techniques well known to those skilled in the artsuch as by sputter deposition, chemical vapor deposition, metal organicchemical vapor deposition, electroplating, electroless plating, and thelike. In some embodiments, the thickness of the one or more conductivetraces 540 is dependent on the particular inductance desired forreceiving conductor structure 500, in order to enlarge the area of thereceiving conductor structure 500. In certain embodiments, each of theone or more conductive traces 540 has a thickness from 0.5 μm to 100 μmor from 25 μm to 50 μm, for example about 25 μm or about 40 μm. In someembodiments, each of the one or more conductive traces 225 has a length(m) of about 5 cm to 200 cm or 50 cm to 150 cm, e.g., about 80 cm. Insome embodiments, the conductive traces 540 are interconnected andconnected to the implantable neurostimulator using one or more vias 545or wiring layers formed within the substrate 535.

In various embodiments, the conductive traces 540 are formed with apredetermined shape to enlarge the area of the receiving conductorstructure 500. For example, the receiving conductor structure 500 maycomprise the one or more conductive traces or wirings 540 formed on thesubstrate 535 in a spiral shape. The spiral shape 545 may includecharacteristics designed to maximize the area of the receiving conductorstructure 500 that can be fabricated on the substrate 535 and fit withinthe size constraint 520 of a delivery mechanism 515 while also takinginto consideration a size of the lossy housing 525 of an implantabledevice 530. In some embodiments, the characteristics of the spiral shapeinclude a predetermined number of turns 550 and a predetermined pitch555 between each of the turns 525 to maximize the overall areaobtainable for the receiving conductor structure 500. In certainembodiments, the spiral shape has 2 or more turns 550, for example from2 to 25 turns, and a pitch 555 between each of the turns from 10 μm to 1cm or from 250 μm to 2 mm, for example about 350 μm. Accordingly, thespiral shape can maximize the area of the receiving conductor structure500 that can be fabricated from the substrate.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to theskilled artisan. It should be understood that aspects of the inventionand portions of various embodiments and various features recited aboveand/or in the appended claims may be combined or interchanged either inwhole or in part. In the foregoing descriptions of the variousembodiments, those embodiments which refer to another embodiment may beappropriately combined with other embodiments as will be appreciated bythe skilled artisan. Furthermore, the skilled artisan will appreciatethat the foregoing description is by way of example only, and is notintended to limit the invention.

What is claimed is:
 1. A medical device comprising: a lossy housingsurrounding a power supply; a receiving coil configured to exchangepower wirelessly via a wireless power transfer signal and deliver thepower to the power supply, wherein the receiving coil is a helicalstructure comprising a plurality of turns having a sequential increasein width; a gap provided between the lossy housing and the receivingcoil on a vertical plane; and a spacer that fills in at least a portionof the gap to maintain the lossy housing a predetermined distance fromthe receiving coil, wherein the spacer surrounds an entirety of thereceiving coil.
 2. The medical device of claim 1, wherein the spacer issilicone, a polymer dispersion, a chemical vapor depositedpoly(p-xylylene) polymer, or a polyourethane.
 3. The medical device ofclaim 1, wherein the spacer is attached to one or more surfaces of thereceiving coil.
 4. The medical device of claim 1, wherein the helicalstructure is three-dimensional and a total rise of the helical structureis determined based on a shape, a number of turns, a pitch of each turn,a helix length, a helix angle, or a combination thereof.
 5. The medicaldevice of claim 1, wherein a width of each of the plurality of turns isless than or equal to a width of the lossy housing.
 6. The medicaldevice of claim 1, wherein a width of a first turn of the plurality ofturns is less than a width of a last turn of the plurality of turns. 7.A medical device comprising: a lossy housing; power supply within thelossy housing and connected to an electronics module; a receiving coilconfigured to exchange power wirelessly via a wireless power transfersignal and deliver the power to the power supply a gap provided betweenthe lossy housing and the receiving coil; and a spacer that fills in atleast a portion of the gap to maintain the lossy housing a predetermineddistance from the receiving coil, wherein the spacer surrounds anentirety of the receiving coil, wherein the receiving coil is a helicalstructure comprising a first turn, a last turn, and one or more turnsdisposed between the first turn and the last turn; and wherein a widthof the first turn is less than a width of the last turn, and wherein theone or more turns have a sequential increase in width from the firstturn to the last turn.
 8. The medical device of claim 7, wherein thereceiving coil is aligned with the lossy housing on a vertical plane. 9.The medical device of claim 7, wherein the receiving coil compriseswound wire formed from conductive material, and the conductive materialis comprised of gold (Au), gold/chromium (Au/Cr), platinum (Pt),platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or anyalloy thereof.
 10. A neuromodulation system comprising: a transmittingconductive structure configured to exchange power wirelessly via awireless power transfer signal; an implantable neurostimulatorincluding: a lossy housing; a connector attached to a hole in the lossyhousing; one or more feedthroughs that pass through the connector; anelectronics module within the lossy housing and connected to the one ormore feedthroughs; a power supply within the lossy housing and connectedto the electronics module; a receiving conductive structure disposedoutside of the lossy housing and connected to the power supply, whereinthe receiving conductive structure is configured to exchange powerwirelessly with the transmitting conductive structure via the wirelesspower transfer signal and deliver the power to the power supply, andwherein the receiving conductive structure is a helical structurecomprising a plurality of turns having a sequential increase in width, agap provided between the lossy housing and the receiving conductivestructure on a vertical plane; and a spacer that fills in at least aportion of the gap to maintain the lossy housing a predetermineddistance from the receiving conductive structure, wherein the spacersurrounds an entirety of the receiving conductive structure, and a leadassembly including: a lead body including a conductor material; a leadconnector that connects the conductor material to the one or morefeedthroughs; and one or more electrodes connected to the conductormaterial.
 11. The neuromodulation system of claim 10, wherein the spaceris silicone, a polymer dispersion, a chemical vapor depositedpoly(p-xylylene) polymer, or a polyurethane.
 12. The neuromodulationsystem of claim 10, wherein the spacer is attached to one or moresurfaces of the receiving coil.
 13. The neuromodulation system of claim10, wherein the helical structure is three-dimensional and a total riseof the helical structure is determined based on a shape, a number ofturns, a pitch of each turn, a helix length, a helix angle, or acombination thereof.
 14. The neuromodulation system of claim 10, whereina width of each turn of the plurality of turns is less than or equal toa width of the lossy housing.
 15. The neuromodulation system of claim10, wherein a width of a first turn of the plurality of turns is lessthan a width of a last turn of the plurality of turns.